TY - JOUR
T1 - Synergystic induction of HIF-1α transcriptional activity by hypoxia and lipopolysaccharide in macrophages
AU - Mi, Zenghui
AU - Rapisarda, Annamaria
AU - Taylor, Lynn
AU - Brooks, Alan
AU - Creighton-Gutteridge, Mark
AU - Melillo, Giovanni
AU - Varesio, Luigi
PY - 2008/1/15
Y1 - 2008/1/15
N2 - Hypoxia Inducible Factor-1 (HIF-1) is activated by a variety of stimuli, including inflammatory mediators. In this report we investigated the role that bacterial lipopolysaccharide (LPS) and hypoxia play in the regulation of HIF-1-dependent gene expression in macrophages. We report that murine macrophages stimulated with low concentrations of LPS (1-10 ng/ml) expressed significantly higher levels of inducible nitric oxide synthase (iNOS) mRNA when cultured under hypoxic compared to normoxic conditions. Functional studies of the iNOS promoter demonstrated that the synergistic interaction between LPS and hypoxia was mediated, at least in part, by the NFκB and the HIF-1 binding sites. In addition, transient transfection experiments using a Hypoxia Response Element (HRE)-containing plasmid showed that LPS and hypoxia synergistically induced HIF-1-dependent transcriptional activity. Interestingly, LPS did not significantly affect HIF-1α protein levels or HIF-1 DNA binding activity relative to hypoxic induction. HIF-1α, but not HIF-2α, was critical for the synergistic induction of HRE-dependent transcriptional activity in macrophages, as indicated by experiments using siRNA targeting HIF-1α or HIF-2α. Addition of ROS-scavengers completely abrogated the synergistic induction of HIF-1 transcriptional activity by LPS and hypoxia, but neither inhibited HIF-1 transcriptional activity induced by hypoxia alone nor affected HIF-1α protein levels or HIF-1 DNA binding induced by hypoxia alone or hypoxia plus LPS. Taken together, our results demonstrate that LPS and hypoxia act synergistically to induce HIF-1α-transcriptional activity and they emphasize the existence of a cross talk between hypoxic and non-hypoxic signaling pathways in the regulation of macrophages gene expression.
AB - Hypoxia Inducible Factor-1 (HIF-1) is activated by a variety of stimuli, including inflammatory mediators. In this report we investigated the role that bacterial lipopolysaccharide (LPS) and hypoxia play in the regulation of HIF-1-dependent gene expression in macrophages. We report that murine macrophages stimulated with low concentrations of LPS (1-10 ng/ml) expressed significantly higher levels of inducible nitric oxide synthase (iNOS) mRNA when cultured under hypoxic compared to normoxic conditions. Functional studies of the iNOS promoter demonstrated that the synergistic interaction between LPS and hypoxia was mediated, at least in part, by the NFκB and the HIF-1 binding sites. In addition, transient transfection experiments using a Hypoxia Response Element (HRE)-containing plasmid showed that LPS and hypoxia synergistically induced HIF-1-dependent transcriptional activity. Interestingly, LPS did not significantly affect HIF-1α protein levels or HIF-1 DNA binding activity relative to hypoxic induction. HIF-1α, but not HIF-2α, was critical for the synergistic induction of HRE-dependent transcriptional activity in macrophages, as indicated by experiments using siRNA targeting HIF-1α or HIF-2α. Addition of ROS-scavengers completely abrogated the synergistic induction of HIF-1 transcriptional activity by LPS and hypoxia, but neither inhibited HIF-1 transcriptional activity induced by hypoxia alone nor affected HIF-1α protein levels or HIF-1 DNA binding induced by hypoxia alone or hypoxia plus LPS. Taken together, our results demonstrate that LPS and hypoxia act synergistically to induce HIF-1α-transcriptional activity and they emphasize the existence of a cross talk between hypoxic and non-hypoxic signaling pathways in the regulation of macrophages gene expression.
KW - HIF-1
KW - Hypoxia
KW - iNOS
KW - LPS
KW - Macrophages
KW - ROS
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M3 - Article
C2 - 18212534
AN - SCOPUS:40549139758
VL - 7
SP - 232
EP - 241
JO - Cell Cycle
JF - Cell Cycle
SN - 1538-4101
IS - 2
ER -